The elusive substance that makes up more than a quarter of the universe is now even more of a mystery. A supersensitive search for dark matter has come up empty, researchers announced in an October 30 press conference, casting serious doubt on the findings of experiments that have claimed detections or hints of dark matter particles.

Dark matter is the ultimate tease: Scientists know it permeates the universe because of its gravitational influence on distant galaxies, but they can’t see it and don’t know what it’s made of. Theoretical physicists have proposed that dark matter could come in the form of weakly interacting massive particles, or WIMPs, and predicted how those particles might behave. Scientists around the world have built giant underground experiments, shielded by soil and rock from the bombardment of other particles, to try to detect WIMPs.

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